Aircraft carburetor



March 29, 1949. G. M. HOLLEY, JR 2,465,535

AIRCRAFT CARBURETOR Filed March 8, 1945 1N VENTOR.

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Patented Mar. 29, 1949 UNITED STATES PATENT OFFICE AIRCRAFT CARBURETOR George Holley, In, Grosse Pointe, Mich., assignor to George M. Holley and Earl Holley Application Mai-c118, 1945, Serial No. 581,644

7 Claims.

The object of this invention is to correct the fuel flow in a pressure type aircraft carburetor for an increase in, (a) altitude and (b) airflow. Specifically the object is to do this for .a variably Venturi carburetor. I

The figure illustrates diagrammatically my invention incorporated .as an airplane carburetor.

In the figure, I is the air entrance, II is the throat of a venturi, I2 is the throttle, WhziChWhEIl moved to the left counter-clockwise, converts the venturi II into a variable venturi, I3 is an opening into the throatof the variable venturi LII-12., thus formed, 14 is a passage connecting the orifice I3 with the chamber I6, I is a passage parallel to and below the passage "I4 and conmeeting the orifice I3 with the chamber I7, I18 is a diaphragm in the chamber I6, :I 9 is a passage connecting the annular chamber 2.0 with a chamber 2| immediately above the diaphragm I8. The annular chamber .2 0 is in communication with the air entrance Ill through a large number of open- .ings 26 so that the pressure of the air entrance exists in the chamber 2|. Springs 22 and "23 support the diaphragm I8, which carries a meter- .ing needle 24, which controls the connection between the chamber I6 and a passage 25.

This pressure of the air entering the carburetor also exists in a similar chamber 21.,in whichthere .is a similar spring 28 and a diaphragm .2 9 corresponding to the diaphragm It, and a spring 30 corresponding to the spring 23 and a metering needle 3| corresponding to the needle 24. needle 3| forms a restricted communication between the chamber I! :and the passage 3-2, which communicates through a restriction 33 with the air inlet pressure line 49. The passage :32 communicates with a chamber 34,, the passage '25 communicates with a chamber '35,, so that Ia diaphragm 31, which separates the chamber 34 from the chamber 36,, is supported on one :side by the pressure in the passage 25 and on the other side by the pressure in the pipe 32,. The pressure in the chamber 34 is higher than the pressure in the chamber 36; that is to say, "the valve 24 is normally opened to such a degree as to admit a good deal of the suction in pipe I4 to the chamber 36., whereas 'the'valve 3A :is normally closed and only opens 'at comparatively high suctions.

The chamber 38 contains a group of altitude bellows 39, which, at altitude, elapandand cause the valve 40 to .move to the left, compressing the ,spring The valve 40, which is a balanced valve, then admits atmospheric air to the passage 2.5, which as stated above 'is a suction passage so that when the bellows 39 expands due to a lowering of the atmospheric pressure in the entrance I0, the pressure in the pipe rises relative to the pressure in the pipe 32, which is not affected by the bellows 39. At altitude, the influence of the air flow on the diaphragm 31 is thus diminished, and the mixture ratio is thus maintained within the desired limits.

The throttle I2 is rotated by the throttle lever '42, which is connected to the link 43, which in its turn is connected to the link 44 to the lever 45. This lever 45' and its control disc '46 are shown turned clockwise into a partially-open throttle position, and in this position, the valve '46 opens the fuel orifices ll and 48, which admit metered fuel to passages 45 and 50. The valve 11 in the automatic lean position, as shown, 0bstructs the flow through the restriction 41 by closing the port I55, but permits that controlled by the opening 48 to flow into the chamber I 53 through port I54. This fuel, together with the small quantity of fuel which flows through a bypass 5I past a low speed adjusting needle 52,, communicates through I53 with the chamber 53 to the right of a diaphragm 54, which is to the right of a chamber 55, which communicates with a fuel entrance through a fuel venturi 51. Hence, the diaphragm 54 is subjected to the pressure drop at the orifice 48, or at orifices ll-48 when valve TI is moved to open port I55 to the automatic rich position. The valve rod 58 em gages through the diaphragm 62 with the pin 59, which engages through the diaphragm 31, and thus with the pin 65, which pin engages through the small diaphragm I56 with the pin 61, the pressure of which is balanced by the passage 144.

In order that the flow shall be regulated, valve 5'8 controls theflow of fuel from an orifice 63 through a passage 64, past valve 58 to a passage 61, which communicates with a chamber 69 below the valve 56. The pressure in the passage 1% and in a chamber is equal to the pressure of the vfuel in the passage 49, except for the escape of the fuel from the passage 64 to a passage 61, the escape of which is controlled by the valve :58. The pressure thus regulated .in the chamber valve 11 moves clockwise, it moves into the idle' cut-01f position; when it moves counter-clockwise, it moves to the automatic rich position (A. R.)

Valve 11 is shown in the automatic lean position. admitted from the variable restriction 41 so that the fuel fiow through both 48 and 41 controls the pressure in chamber 53. This is the automatic rich position (A. R.)

Valve I7 and link 19 are connected through the link 84 to the lever 85, which controls the rotation of the valve 86. In the position shown, in which the mixture control valve 11 closes port I55 and thus the valve 46 admits fuel only through the passage 49, the valve 86 provides a path from the pipe 81 to the L-shaped passage 88, which communicates with the passage 89 and also with the passage 99. These passages 89 and 99 com municate through the restriction 9I and through the restriction 92 to the passage 93, and so to the chamber 94, which communicates with the cham-- ber 69, so that any fuel flowing through the passage 93 is added to the fuel flowing past the restriction 48. This fuel flowing through 81 flows I from the chamber 95 to the right of the diaphragm 96, which chamber 95 communicates with the fuel entrance 56 through the passage 91.

The chamber 98 to the left of diaphragm 96 communicates with the throat of the venturi 51 through the restricted orifice 99. Valve I99 is carried by the diaphragm 96 and is seated by a compression spring I9I in chamber 98 so that the flow through the venturi 51 must be great enough to compress the spring I9I; otherwise, the valve .I 99 will not open, so that the valve I99 only opens at high air flows and when the fuel flow is correspondingly high.

A passage I92 connects with the restricted orifice 99, and in the position shown is inoperative. When the lever 85 is moved counter-clockwise into the automatic rich position (A. R.), an opening I93 in 86 allows the fuel flowing through 99 to flow through I93 from a restricted passage I9 4. The jet numbered I69, located in the passage I94 is an important restriction in the fuel metering system. Restriction 99 is inserted only to make the jet I69 of small enough size. Jet 99 causes the valve I99 to move to the left to open is no longer as powerful because of the back bleed from I94 through I93 up I92 through 99 to the throat of venturi 51. I

When anti-detonatin liquid is required to obtain military output, the usual practice is to cut off the fuel added by the power enrichment venturi 51, valve I99 and passages 81, 99, 99 and 93. The pressure of this anti-detonation liquid, water for example, is applied through a passage I95 to a chamber I96, containing a diaphragm I91.

I This compresses a spring I98 contained in cham- When rotated anti-clockwise 45, fuel is s can be omitted if the suction holes in the Venturi throat 51 are of the proper size and are held .close limits in production.

The passage I94 communicates with the unmetered fuel in the chamber 55 so that when the lever is moved counter-clockwise to the automatic rich position (A. R), a certain amount of fuel flows from the chamber 55 through the passage I94 through the restricted orifice I69 to the passage I92, and so the pressure in the chamber 98 rises. Hence, the valve I99 closes slightly, and the combined effect of rotating the lever 85 counter-clockwise is to open valve 11 so as to admit fuel from port 41 and by rotating valve 86 to cut oil the fuel flowing through 89 and restrict the fuel to the capacity of the restriction 9|. In addition, the operating pressure difference which her 94. The diaphragm I91 is adapted to close the end of the passage 93 so that when antidetonating fluid is added, no fuel flows through passage 93, except through a small side hole II. The anti-detonating liquid is contained in tank I6I. The pipe I62 is connected with some convenient source of pressure, for example, the fuel entrance 56. anti-detonatin fluid to issue from the nozzle I64.

Acceleration When the throttle I2 is opened rapidly, the lever II9, connected to the throttle I2 and lever 45 by links 43 and 44, is rotated clockwise and supplies pressure through the cam III to the finger II 2, which moves the diaphragm II3 to the right. chamber II4, which unseats the valve II5 and allows accelerating fuel to discharge through the discharge orifice II6 on the engine side of the throttle I2. Valve II5 is carried by a diaphragm 1, which forms the opposite wall of the chainber formed by the two diaphragms H3 and III. A restriction II8 determines the time the valve II5 remains open. The compression spring I 29 also determines the time the valve II5 remains open. The accelerating fuel is supplied from the pipes 82 andBI, which are connected with the passage 97.

Passages BI' and 82 are connected through the passage 83 in the valve .11. When the valve I1 is moved 45 into the idle cut-ofi position, the passage 83 moves clockwise and leaves the two passages BI and 82 cut off from each other. The object of this is that when the attempt is made to stop the engine by placing the valve in the idle cut-01f position, the attempt has failed. The instructions are that when the throttle I2, which is in the position to give approximately 1950 revolutions per minute, is opened, thus flooding the engine with air and rendering the mixture non-explosive, the accelerating device shown will automatically function unless the pipe 9| was cut off from the pipe 82, and it is most undesirable when stopping an engine for the accelerating device to discharge fuel. Moreover, as the engine slows down, the pressure in the pipe 8I automatically falls, which also is apt to cause the untimely discharge of fuel from the accelerating device.

To sum up, the wobble pump can be used as a primer when the valve I1 is in the automatic rich position (A. R.). It can also be used when in the automatic lean position, but it cannot be used when in the idle cut-ofi position.

The unmetered fuel in the chamber 55 and the chamber 53 containing metered fuel are both vented either back to the tank, or as shown through the passage I28 through the restriction I 29 to the outlet I39 of the venturi I3I2. The vapor is thus removed from the upper part of the chambers 53--55. Floats I3I-I32 have integral with them valves which control outlet orifices.

Valve I63, when opened, causes This compresses the liquid in the The passage I is the alternative escape back to the tank.

Passage I36 communicates with the air emtrance I0 and with the chamber III to the left of diaphragm 62 and also with the drain passage I38. Passage I36 also communicates with the chamber I46 to the right of diaphragm I56, and chamber I 40 also communicates with the drain passage I38. The restriction I 42 in the drain passage I38 communicates with the suction pas sage I43, which communicates with the outlet passage I30, down which any liquid escaping by the valve 58 or past the rod BI is drawn into the engine. A passage I44 connects the chamber I45 to the right of the end of the pin 6! and communicates with the unmetered fuel in chamber 55. The passage I9 communicates with the passage I46, which communicates with the chamber I on the left-hand side of the diaphragm I56. The passage I46 also communicates with the right-hand side of diaphragm 62, that is, with chamber I49, so that the diaphragms 62 and I56 have the same pressure on each side.

Operation Assume that the engine is running with the controls as shown in the cruising lean position, but with the throttle I2 not fully open.

The fuel flow from the entrance 56 past the diaphragm 54 through the restriction 48 will control the pressure difference on the opposite sides of the diaphragm 54 as the right-hand side of 54 communicates with the downstream side of restriction 46. The valve 11 will completely close the opening I55 so that the flow through 41 is blocked when the controls are in the position shown.

The flow through the air entrance creates a pressure difierence between the entrance openings 26 and the opening I3 in the throat. This pressure difference, assuming that the plane is flying at sea level and the valve 40 is closed, is transmitted through the pipe I4 past the valve 24 through passage 25 to chamber 36 on the left= hand side of the diaphragm 37.

The atmospheric pressure is transmitted through the passage I9 through the restriction 33, passage 32 to the chamber 34 on the righthand side of the diaphragm 37. Assume that the air flow is out of step with the fuel flow, as happens when the throttle is partly closed, so that an excessive amount of fuel is flowing. Then the pilot valve 58 is moved to the right by the pressure drop through restriction 48 actmg on diaphragm 54, and the flow through passage 64 ceases. Then the pressure in chamber 65 rises and valve 66 moves to restrict the flow past the valve 66. This restricted flow causes the valve 53 to move to the left to reopen. This increases the flow past this valve 58 through passage 64 and this causes a drop in pressure, which permits the valve 66 to open more so as to increase fuel flow and thus reestablish equi llbrium.

The pins 58-59, so and SI are separated by the diaphragms 62, 31 and I56, and any leakage past the pin 6| or 58 will not now past the pins 59 and 60, but will flow past the restriction I42 in the pipe I38--I43.

As the flow of air increases, the velocity exceeds the critical and the valve 8| is moved down and thus lowers the pressure in the pipe 32 and thus reduces the fuel flow. The air is an elastic medium so that as the velocity reaches the critical, the depression is. greater than the in 6 crease in the weight of air taken in would justify so that without the valve -3I, the mixture would get rich. The pressure d-ifierence across the di aphragm 31 being balanced against the pres= sure difference across the diaphragm 54 controls fuel flow.

As the plane ascends, the barometric element 39 expands and air flows from the opening 26 past the valve 40 to the passage 25 to the cham ber 36 and thus reduces the pressure difierence across the diaphragm 31. The same weight of air per second causes a greater drop in any venturi, the less the density. that is, the greater the altitude. Hence, the valve 40 corrects for altitude in conjunction with valve 24. The variable openin past the valve 3! in conjunction with the fixed restriction 33 prevents the mixture becoming abnormally rich when the airflow becomes very great. The variable opening past the valve '24 in conjunction with the openin around the valve 46 prevents the mixture from becoming rich at high altitude. At any given altitude the opening around the valve 40 is fixed although this opening varies at every altitude, hence, at any given altitude the degree of compensation for altitude is obtained by the variable opening around the valve 24 and the fixed opening around the valve 43. The pressure drop across the valve 46 is determined by the amount of air drawn past the valve 24. The amount of this air is controlled by the valve 40. At high velocity of airflow into the engine past the throttle valve I2 causes the valve 24 to open and the increased air now past the valve '24 causes an increase in the pressure drop in the pi e 25. This is the pre sure drop past the valve '46 and this pressure drop is determined by the barometric element 39 and is transmitted to the low pressure side of the diaphragm 31. An increase in this suction causes an increase in fuel flow. A

' decrease in fuel flow is caused by an increase in air now past the valve 3I as the suction in the pipe 32 is transmitted to the pressure side of the diaphragm 31.

What I claim is:

1. A fuel supply system for an engine comprising an air intake, a variable streamlined restriction in said intake, a fuel supply passage, a supply of fuel under pressure, a variable fuel restriction therein, means for simultaneously opening and closing said variable air restriction and said variable fuel restriction, the variable fuel restriction being designed to be approximately half open when the variable streamlined restriction is half open and to fully open only when the variable streamlined restriction is fully open, automatic fuel "control means for maintaining a predetermined mixture ratio including two diaphragms, one responsive to the drop in pressure due to fuel flow through said fuel restriction, the other 'responsiv'e to the drop in air pressure in the throat of said variable restriction, a pilot valve engag ing with and operated by both diaphraglns act mg in opposition to each other, a fuel metering valve in said fuel passage controlled by said ilot and located in series with and downstream from said variable fuel restriction, a fuel bypass around said metering valve leading past said pilot valve, a restriction in said bypass located upstream from said pilot valve, a diaphragm engaging with said metering valve, spring means adapted to close said metering valve, the change in pressure in said bypass responsive to the movement of said ilot valve being adapted when applied to said diaphragm to open and close S'Eid meter-ingvalve v7 whereby the drop in pressure across said variable fuel restriction is adjusted so as to equal the drop in pressure at the throat of said variable air restriction.

2. A carburetor having an air entrance, an air venturi therein, a source of fuel under pressure, a fuel entrance leading to a fuel metering restriction, a first flexible diaphragm responsive to the pressure drop across said metering restriction, a second flexible diaphragm engaging with and opposing the movement of the first diaphragm and responsive to the pressure drop in the throat of the said air venturi, a pilot valve adapted to be operated by said two diaphragms, a fuel pressure regulating valve located downstream from the said fuel metering restriction, fluid pressure operating means for said pressure regulating valve controlled by said pilot valve, altitude correcting means for the pressure drop in the throat of the said air venturi comprising a passage leading from the throat of the said venturi to the suction side of said second diaphragm, a valve in said passage a third diaphragm responsive to the pressure drop in said venturi and to yielding means operating in opposition to said pressure drop connected to said last mentioned valve, an atmospheric air bleed leading into said passage between the valve and the suction side of said second diaphragm, a valve in said bleed, barometric means for opening said last mentioned valve at high altitude, air flow correcting means for the pressure drop in the throat of said air venturi comprising a passage connecting the pressure side of said second diaphragm with the atmospheric pressure in the air entrance, a restriction therein of a fixed size, a venturi suction bleed into said passage located between "said restriction and the pressure side of said second diaphragm, a valve in said bleed, a fourth diaphragm connected to said last mentioned valve and also responsive to the pressure drop in said venturi and to yielding means opposing said pressure drop. 1

3. A carburetor having an air entrance, an air venturi therein, a source of fuel under pressure, a fuel entrance leading to a fuel metering restriction, a first flexible diaphragm responsive to the pressure drop across said metering restriction, a second flexible diaphragm engaging with and opposing the movement of the first diaphragm and responsive to the pressure drop in the throat of the said air venturi, means for restricting the flow of fuel through said fuel metering restriction controlled by the movement of said first and second diaphragms, altitude correcting means for the pressure drop in the throat of the said air venturi comprising a passage leading from the throat of the said venturi to the suction side of said second diaphragm, a valve in said passage a third diaphragm responsive to the pressure drop in said venturi and to yielding means operating in opposition to said pressure drop connected to said last mentioned valve, an atmospheric air bleed leading into said passage between the valve and the suction side of said second diaphragm, a valve in said bleed, barometric means for opening said last mentioned valve at high altitude, air flow correcting means for the pressure drop in the throat of said air venturi comprising a passage connecting the pressure side of said second diaphragm with the atmospheric pressure in the air entrance, a restriction therein of a fixed size, a venturi suction bleed into said passage located betweenzsaid restriction and =-the pressure: side of said second diaphragm, a valve in said bleed, a fourth diaphragm connected to said-last mentioned valve and also responsive to the-pressure drop in said venturi and to yielding means opposing said pressuredrop.

4. A device as set forth in claim '2 in which the fluid pressure operating means for the pressure regulating valve is derived from the fuel supply downstream from said fuel metering restriction. 5. A carburetor having an air entrance, variable streamlined air restriction forming a venturi therein, a source of fuel under pressure, a fuel entrance leading to a variable fuel metering restriction operatively connected to said streamlined air restriction, a first flexible diaphragm responsive to the pressure drop across said variable metering restriction, a second flexible diaphragm engaging with and opposing the movement of the first diaphragm and responsive to the pressure drop in the throat of the said air venturi, a pilot valve'adapted to be operated by said two diaphragms, a fuel pressure regulating-valve 1a: cated downstream from thesaid fuel metering re- A striction, fluid pressure operating means for said pressure regulating valve controlled by said pilot valve, altitude correcting means for the pressure drop in the throat of the said air venturi comprising a passage leading from the throat of the said venturi to the suction side of said second dia-'- phragm, a valve in said passage a third diaphragm being responsive to the pressure drop in said venturi and to yielding means operating in opposition to said pressure drop connected to said last mentioned valve, an atmospheric air bleed leading into said passage located between the valve and the suction side of said second diaphragm, a valve in said bleed, barometric means for opening said last mentioned'valve at high altitude, airflow correcting means for the pressure drop in the throat of said air venturi comprising a passage connecting the pressure side of said second diaphragm with the atmospheric pressure in the air entrance, a restriction therein ofa fixed size, a venturi suction bleed into said passage located betweensaid restriction and the pressure side of said second diaphragm, a valve in said bleed, a fourth diaphragm connected to said last mentioned valve and also responsive to the pressure drop in said venturi and to yielding means opposing said pressure drop.

' 6. A device as set forth in claim 5 in which'the fluid pressure operating means for the pressure. regulating valve is derived from the fuel supply downstream from said fuel metering restriction.

7. A carburetor having an air entrance, vari-f able streamlined air valve forming a venturi therein, a source of fuel under pressure, a valve forming a variable fuel metering restriction, a fuel entrance leading to said variable fuel metering valve, mechanical linkage connected to said valve operatively connected to said streamlined air valve, a first flexible diaphragm responsive to the pressure drop across said variable metering, restriction,, a second flexible dia-.'

9 throat of the said venturi to the suction side of said second diaphragm, a valve in said passage a third diaphragm being responsive to the pressure drop in said venturi and to yielding means operating in opposition to said pressure drop connected to said last mentioned valve, an atmospheric air bleed leading into said passage located between the valve and the suction side of said second diaphragm, a valve in said bleed barometric means for opening said last mentioned valve at high altitude, air flow correcting means for the pressure drop in the throat of said air venturi comprising a passage connecting the pressure side of said second diaphragm with the atmospheric pressure in the air entrance, a restriction therein of a fixed size, a Venturi suction bleed into said passage located between said restriction and the pressure side of said second diaphragm, a valve in said bleed, a fourth diaphragm connected to said last mentioned valve and also responsive to the pressure drop in said venturi and to yielding means opposing said pressure drop.

GEORGE M. HOLLEY, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

